Diene elastomers such as polybutadienes and butadiene styrene copolymers are employed for manufacture of tire treads of automobiles. Recently, demands for elastic materials showing low rolling resistance and high road gripping property have been increased for the manufacture of tire treads, from the viewpoints of reduction of fuel consumption and increase of driving performances on snow-covered roads and ice-covered roads.
It has been proposed to introduce specific functional groups into the elastic material by reacting the elastic material having alkali metal atoms with a reactive compound so as to impart the required characteristics to the elastic material. Until now, however, there are not provided satisfactorily modified elastic materials. Particularly, the modified elastic material produced by the known reaction is unsatisfactory in that it has low cis-1,4 unit contents in its molecular structure and shows abrasion resistance lower than that of elastic material having a high cis unit content.
It is known that an elastomer having a high cis-unit content is reacted with an elastomer-modifying agent in the presence of a catalyst in an elastomer solution to give a modified elastomer. For instance, Japanese Patent Provisional Publication No. 58-142901 describes modification of elastomer by reacting an unsaturated bond-containing elastomer with an organic compound having a carboxyl group and an aldehyde group in an elastomer solution in the presence of an acid catalyst. Japanese Patent Provisional Publication No. 58-162602 describes a reaction of an unsaturated bond-containing elastomer with an organic compound having a carboxyl group and a salt of an aromatic sulfone-haloamide in an elastomer solution to give a modified elastomer. Japanese Patent Provisional Publication No. 61-225202 describes modification of elastomer by reacting an unsaturated bond-containing elastomer with an elastomer-modifying organic compound such as benzylidene butylamine or an organic acid halide in an elastomer solution in the presence of a Lewis acid catalyst.
As described above, most of known processes for the elastomer-modification necessarily employ an organic solvent for preparing the elastomer solution from a once isolated elastomer. It is not advantageous to produce the modified elastomer from the isolated elastomer, and it is preferred to modify an elastomer in its reaction mixture (i.e., without isolation) to obtain the desired modified elastomer. It also is a problem that the amount of the solvent employed for the preparation of an elastomer solution is quite large. The use of such a large amount of an organic solvent is disadvantageous from the viewpoint of the industrial production of modified elastomers.
It is known that transition metal catalysts such as Co-containing catalyst, Ni-containing catalyst, Ti-containing catalyst, and Nd-containing catalyst is favorably employable for preparing an elastomer having a high cis-unit content. However, the elastomer prepared using one of the Co-containing catalyst, Ni-containing catalyst and Ti-containing catalyst is not living, namely, not a living polymer, and hence it is difficult to modify the non-living polymer with an elastomer-modifying agent.
In contrast, the Nd-containing catalyst can give a pseudo-living elastomer in the preparation of diene polymer, which can be modified with an elastomer-modifying agent. For instance, Japanese Patent Provisional Publication No. 63-178102 describes the modification of a polymer prepared from a conjugated diene in the presence of lanthanide rare earth metal catalyst with a specific organometal halide. The modification reaction is performed just after the diene polymer is prepared. Japanese Patent Provisional Publication No. 63-297403 describes a process for preparing a modified diene polymer which comprises a step of producing a polymer from a conjugated diene in the presence of a lanthanide rare earth metal catalyst and a step of immediately reacting the polymer with a specific hetero-cumulene compound or hetero-three-membered cyclic compound. Japanese Patent Provisional Publication No. 63-305101 describes a similar process for preparing a modified diene polymer using a specific halogen-containing compound such as 2,4,6-trichloro-1,3,5-triazine as the modifying agent.
The use of a lanthanide rare earth metal catalyst can give a pseudo-living diene polymer which is easily modified to obtain the desired modified elastomer. However, the polymerization reaction using the lanthanide rare earth metal catalyst is low in its reaction rate per the amount of catalyst, as compared with the case using a Co-containing catalyst. The Co-containing catalyst has been believed not to give a living or pseudo-living polymer after polymerization of a diene compound.